Autobiography of Sir John Rennie, F.R.S. 32

Autobiography of Sir John Rennie, F.R.S. 32

of time and money as to the best mode of accomplishing it. One object

should be as far as practicable to reduce the extent of main or barrier

banks, and if the situation be well adapted for the purpose, a barrier

bank may be commenced at the lower end, and gradually pushed forward in

proportion as the space above it exhibits a tendency to silt up; in

combination with this the minor operations should be carried on, so that

the one may assist the other. When a sufficient quantity of marsh above

the barrier bank has been formed, it may be embanked from the sea, and

by keeping the barrier bank always sufficiently in advance the interior

banks will become less costly, as they will not be exposed to the main

force of the waves during storms; otherwise each separate bank must be

made a barrier bank, and the whole cost will be materially increased. The

propriety of adopting either the one system or the other will greatly

depend upon the peculiar local circumstances.

 

With regard to the quantity of land, when fit for the purpose, to be

embanked or enclosed at one time, this also will, like the other,

depend upon the local circumstances. Generally speaking it is safer to

confine the operation to about 400 or 500 acres; and the proper time for

closing the embankment is during neap tides, when the work will be much

facilitated.

 

It is true that much greater quantities may be taken in at one time,

according to the Dutch system, but then several closing spaces must be

left open, and these must all be specially prepared for the purpose by

lining the bottom and sides with wicker-work and fascines to prevent the

scour, and then filling them up with clay, stone, fascines, and earth,

as the case may require; and if by chance a breach should take place,

which occasionally occurs under the best of management, the internal

space to be filled with water is so great that the violence and strength

of the inpouring current is increased in the same proportion, so that it

carries all before it, scoops out great channels in the interior space,

and damages the land by the great quantity of sand brought in, and it

becomes difficult to clear the internal space of water. And although by

this plan a less quantity of embankment is required, nevertheless the

expense per lineal foot becomes greater; but where the length of the

embankment is small compared to the depth of the land to be enclosed,

this system, if properly managed, may be adopted with advantage. The most

advisable plan must be left a good deal to the judgment and skill of the

engineer-in-chief taking advantage of the local circumstances.

 

The above principles for warping and enclosing land I recommended in

several reports to the Norfolk Estuary Company, but they were not adopted

to the extent I recommended; the consequence has been that several

years’ time and a good deal of money have been unnecessarily expended.

But I believe that they have been finally convinced that my system was

the proper one, and it has since been adopted to some extent, with

considerable success, and about 1000 acres (in 1867) have been enclosed,

the property of the Company, at the cost of about 15_l._ per acre, the

land being worth 40_l._ They have, moreover, enclosed 600 acres more

for the Prince of Wales, upon which they will be paid one-third of its

improved value. As several thousand acres in the estuary belonging

to the Company are rapidly approaching that state when they may be

profitably embanked, I confidently believe, by proper management, that

the shareholders will ultimately recover a good deal if not the whole of

their capital, and perhaps a good portion of their interest also; but I

shall always contend that if my recommendations had been followed from

the beginning, a great deal of money would have been saved. The Company

ought not to have submitted to the restrictions imposed by the Acts. The

contribution from the drainage and navigation interests ought to have

been double, for which they would have been amply repaid, and the land

gained would have been far greater, so that even by this time it might

have been a very profitable concern.

 

Whilst the Nene Outfall was in progress, I was employed by the

Corporation of Boston to improve the outfall of the river between the

Grand Sluice at the upper end of the town, and Hobhole near the mouth

of the river, a distance of nearly four miles. This had previously

been proposed by my father, in the year 1845, to the Corporation of

Boston, previous to commencing the great drainage of the East, West,

and Wildmere fens bordering upon the Witham between Lincoln and Boston,

amounting to about 125,000 acres of lowland, which for the most part was

little better than a marsh. It was here he proposed his grand system for

the drainage of lowlands by means of catchwater drains for the waters

from the highlands, and main and minor drains for the waters from the

lowlands, both systems of drains being distinct and separate from each

other, and which he afterwards most successfully carried into effect. In

order to obtain the requisite fall, it was necessary that the outfalls

of the two main drains should be carried into the Witham below the

town of Boston; but in order that this might be effectual, it was also

necessary that the Witham should be greatly improved between Boston and

the mouth at Hobhole; and as the navigation between these two points

was very defective, he thought that the Corporation should bear the

expense, as they would derive the greatest benefit. For this purpose my

father proposed two plans: one was to improve the old channel, partly

by cutting off the bends and confining and straightening its course,

and from Hobhole making a new cut to Clayhole, where there was ample

depth of water at all times of tide; and the other plan was to make a

direct cut within land from the lower end of Boston to Clayhole. He

proposed also, for the drainage, to make an outfall for the highland

water at Maudfoster, just below the town of Boston, as he said that by

bringing the highland water there, it would effectually serve to keep

the river open between that point and its mouth at Hobhole, and to make

an outfall for the lowland waters at the latter place; and he recommended

the drainage interests to contribute a certain portion of the expense

towards the improvement. The Corporation of Boston declined doing

anything, and the drainage was left to take care of itself. Mr. Rennie,

however, foresaw that if the Witham was not improved by either one or

the other of the plans that he recommended, the highland water would not

be effectively discharged by the sluice at Maudfoster, and therefore he

made a communication between the Maudfoster drain and the Hobhole drain

at a place called Cowbridge, a few miles above Boston, where there was a

gauge, so that whenever the water in Maudfoster drain exceeded the gauge

it passed into the lowland main drain, and from thence into the Witham at

Hobhole. What Mr. Rennie foresaw came true; the Witham, not having been

improved, became worse, and the river in front of the Maudfoster Sluice

was silted up, so that it could not discharge its water, and therefore

the whole of the water, highland and lowland, was obliged to go by

Hobhole, which drain and sluice, foreseeing what would take place, he had

enlarged for the purpose.

 

In the year 1827, the outfall of the Witham between Boston and Hobhole

had become so much silted up that at high water of neap tides there was

scarcely water enough for fishing boats to come up to the town during

the summer months and dry seasons, and at spring tides only sloops

of very small draught could get up to the town; in fact, it might be

said that at that time Boston as a seaport was lost, and the trade and

navigation of the port ruined. At this the Corporation became greatly

alarmed, and sent for me. I directed the late Mr. Francis Giles to make a

complete survey of the river, which he did in his usual able and correct

manner, and no person could do it better. Being provided with this

survey, I made my report, and saw clearly that there was no remedy but

to carry into effect either the one or the other of my father’s plans

of 1805. As the Corporation funds were very limited, I recommended the

plan for improving the old channel, partly by cutting off the bends and

confining the river as far as Hobhole, and from thence making a new cut

to Clayhole, as recommended by my father. There were three parties who

were to contribute towards the improvement of the outfall of the Witham,

namely, the Corporation of Boston, and the Witham and the Black Sluice

Commissioners. The Black Sluice Commissioners demurred to the plan

proposed by me, which was my father’s, on the ground that the cut ought

to be made from the Black Sluice inland direct to Hobhole, otherwise

they would not derive the advantages they had a right to expect from

their contributions; so the whole matter was referred to Mr. Telford,

who said that no improvement in the river below Boston would be of any

use, unless the Grand Sluice above Boston was removed, so as to admit the

tide to flow farther up the river. Now, although Telford was to a certain

extent right, but by no means wholly so, because by carrying into effect

either of my father’s plans there could be no doubt that considerable

improvement would be made on the outfall of the Witham below Boston,

as the sequel will show, nevertheless, if the Grand Sluice had been

removed the tide would have flowed farther up the river and the increased

quantity of tidal water passing upwards and downwards would have improved

the outfall still further; but there were insuperable objections to

the removal of the Grand Sluice, which neither of those parties above

mentioned who were to make the improvement in the outfall could control,

for the river above the Grand Sluice was under a different body. The

banks must have been raised to admit the tide; compensation must have

been made for the loss of fresh water, and various other interests must

have been consulted that were hostile. The Black Sluice Commissioners

stuck to Telford’s report, and withdrew from the contribution, so that

the whole matter fell to the ground.

 

The outfall of the Witham became worse, and the Corporation of Boston,

being left single-handed, and having determined to do what they could to

improve the river, again requested my advice. I said that the best thing

they could do under the circumstances would be to carry into effect by

degrees, as far as their means would allow, the plan of my father already

referred to for improving the old channel of the river, and to begin by

cutting off the bend between Hobhole and the upper end of Burton’s Marsh

(this cut would be about half a mile long), and blocking up the old

channel immediately above it, which was about half a mile wide. These

two works would shorten the navigation quite half a mile, and admit and

discharge the tidal and fresh waters more readily, and thus produce a

corresponding scour and lowering of the low-water line and bed of the

river all the way up to the Grand Sluice above Boston.

 

The Corporation adopted my recommendation, and entered into a contract

with Jolliffe and Banks for that purpose. Although a small work, it

was attended with considerable difficulty, particularly in closing the

old channel, on account of its great width and the great body of tidal

water which passed through it. The effect of this work exceeded my most

sanguine expectations; in a short time it improved the channel upwards

to Boston to such an extent that spring tides rose at Boston Bridge 14

feet, and neaps 10 feet, and the bed of the river was deepened from 3

to 4 feet below low water of springs, so that vessels drawing 15 feet

and 16 feet could come up to the town at springs, and vessels drawing 12

to 13 feet could come up at neaps; moreover, all the silt was scoured

away from the front of the Maudfoster Sluice, so that it discharged the

highland water from the fens, which it had not done for years before,

and improved also the discharge of the waters from the Grand and Black